1. Technical Background of the Invention
The present invention relates to a magneto-electric device for use in a magnetic sensor for detecting the number of revolutions of a gear or the like and a manufacturing method therefore.
2. Related Art
In recent years, intelligent household electrical products, industrial machines and automobiles have appeared, causing improvement in a variety of sensor techniques to be required. A hall device which is one of magnetic sensors, is able to output a voltage signal corresponding to the magnetic field. Since the hall device, which is a non-contact type device, is highly resistant against contamination. The hall devices have widely been used. For example, a magnetic sensor incorporating the hall device is employed in a vehicle, such as an automobile, to serve as a rotation sensor for detecting the number of rotation of a gear or the like.
In the foregoing case, the hall device is disposed between a gear (which must be detected) having projections and depressions, and a bias magnet. Thus, an external magnetic field from the bias magnet penetrates the hall device and moves to the surface of the gear having the projections and depressions. Hence it follows that the hall device produces an output of a voltage signal corresponding to the magnitude of the external magnetic field.
When the gear having the projections and depressions has been rotated, the magnetic field is changed due to the projections and depressions of the gear. It leads to a fact that also the magnetic field which penetrates the hall device is changed. The change in the magnetic field causes the voltage signal extracted from the hall device being changed. As a result, the number of revolutions of the groove can be detected in accordance with the change in the voltage signal.
When the sensitivity of the hall device is unsatisfactorily low, a proper output of the detected voltage cannot be obtained. To improve the sensitivity of the hall device in a weak magnetic field, a hall device provided with a magnetic collector has been suggested. FIG. 10(a) is a schematic view showing the hall device provided with a magnetic collector. FIG. 10(b) is a side view. As can be understood from FIGS. 10(a) and 10(b), a hall device body 101 formed by a compound semiconductor is formed on a sub-slate formed by NiZn ferrite. Moreover, input/output terminals 107, 108, 109 and 110 are connected to four lead frames 105.
A top jacket 111 constituted by a magnetic collector in the form of a square magnetic member or a cylindrical magnetic member is disposed on the upper surface of the hall device body 101. The top jacket 111, the sub-slate 103 and the lead frames are secured by adhesive agent 113. The top jacket ll converges an external magnetic field to the hall device body 101 so that the sensitivity of the hall device in a weak magnetic field is improved.
In JP Hei.7-198433A, an area flow meter has been disclosed which incorporates a magnetic sensor provided with the magnetic collector. The magnetic sensor provided with the magnetic collector is shown in FIGS. 11(a) and 11(b). A magnetic collector 127 made of such as permalloy exhibiting excellent permeability formed into a tapered shape is provided for each sensitive surface of the hall device A which is the magnetic sensor. Thus, the magnetic field generated by a magnet is captured by the magnetic collector 127. The captured magnetic field is converged to a base portion of the magnetic collector 127, the base portion having a small diameter. Thus, sensitivity is improved. As a result, the magnetic field is converged to the sensitive surface of the hall device, causing the output of the hall device to be enlarged.
In JP.Sho.59-154085A, a magneto-resistance effect device has been disclosed. The disclosed magneto-resistance effect device incorporates a magnetic collection pattern constituted by a thin ferromagnetic film having, high permeability. The magnetic collection pattern is disposed adjacent to a sensor pattern which is used to detect change in the electric resistance, the magnetic collection pattern being disposed while electric insulation being Maintained through a thin insulating film.
The magneto-resistance effect device disclosed in JP.Sho.59-154085A is effective when it is employed as a ferromagnetic magneto-resistance effect device. The ferromagnetic magneto-resistance effect device includes magnetic members disposed such that the sensor surface has sensitivity in the horizontal direction. On the other hand, a satisfactory effect cannot be obtained from a structure, such as a hall device, in which the surface of the device has sensitivity in the vertical direction.
Each of the hall devices shown in FIGS. 10 and 11 requires an afterward process for bonding the magnetic members to the hall device. It leads to a fact that the overall thickness of the sensor is undesirably enlarged. Moreover, a complicated operation must be performed when each of the magnetic members must be joined to the hall device. As the size of the hall device is reduced, the operation for bonding the magnetic members becomes difficult. Therefore, productivity of the hall devices has been unsatisfactorily low.
Accordingly, the applicant of the invention has applied a magneto-electric device and a manufacturing method therefor in Japanese Patent Publication No. Hei.11-261131 to solve the above-mentioned problems.
As shown in FIG. 12, the magneto-electric device includes: a silicon substrate 211; and a hall device portion 215 formed adjacent to the surface 213 of the silicon substrate 211 and capable of outputting an electric signal corresponding to the magnitude of the external magnetic field. Moreover, the magneto-electric device incorporates an etched groove 219 which is formed on the reverse side 217 of the silicon substrate 211 at a position opposite to the hall device portion 215. The etched groove 219 is formed into a tapered shape, the diameter of which is gradually reduced as the distance from the reverse side 217 to the hall device portion 215 is shortened. In addition, the magneto-electric device includes a magnetic film 223 formed on the surface of the etched groove 219 and exhibiting a high permeability so as to converge the external magnetic field to the hall device portion 215.
The magneto-electric device having the above-mentioned structure causes the external magnetic field to be converged to the hall device portion 215 due to the magnetic film 223 formed on the surface of the tapered groove. Since the structure is arranged such that the vertical magnetic field is converged to both of the right side and the reverse side of the hall device portion 215, it permits the sensitivity of the hall device to be improved even in a weak magnetic field.
The hall device portion 215 is formed in the silicon substrate 211. Moreover, the magnetic film 223 is formed in the etched groove 219. Thus, excessive enlargement of the thickness from that of original silicon substrate 211 can be prevented. Hence it follows that the size of the device can be reduced. Since a multiplicity of devices and the magnetic film, which must be formed, can be formed on the silicon substrate, the productivity of the hall device can be improved.
Recently, there is a requirement for the conventional magneto-electric device portion of the foregoing type to improve the effect of converging the magnetic field and the sensitivity of the magneto-electric device in a weak magnetic field.
An object of the present invention is to provide a magneto-electric device which is capable of furthermore improving the sensitivity in a weak magnetic field by improving the effect of converging a magnetic field to the magneto-electric device portion and a manufacturing method therefor.
To achieve the above-mentioned problems, the present invention is provided with a magneto-electric device including:
a first semiconductor wafer including a first surface and a second surface opposite to the first surface;
a magneto-electric device portion provided to the first surface;
a first groove portion recessed from the second surface toward the first surface;
a first magnetic film formed on the second surface and the surface of the first groove portion;
a second semiconductor wafer including a third surface and a fourth surface opposite to the third surface, the second wafer provided so that the magneto-electric device portion is interposed between the first and fourth surfaces;
a second magnetic film formed on the second wafer and located opposite from the first wafer with respect to the magneto-electric device portion;
a bonding portion for bonding the second wafer to the first surface side;
wherein a width of the first groove portion becomes short toward the magneto-electric device portion;
wherein the second magnetic film includes a projection which project toward substantially perpendicular to the third and fourth surfaces;
wherein a second groove portion is etched from the third surface toward the first wafer, the second magnetic film is formed on the second groove portion;
wherein the second groove portion is formed into a trapezoidal shape by anisotropic etching;
wherein a bottom of the second groove portion is located adjacent to the magneto-electric device portion;
wherein a surround recess portion is etched from the forth surface, the surround recess portion surrounds a wafer projection of the second wafer, the second magnetic film is formed on the wafer projection;
wherein the wafer projection is formed into a trapezoidal shape, the surround recess portion is etched by anisotropic etching;
a width of the wafer projection becomes short toward the magneto-electric device portion.
The above-mentioned magneto-electric device has the structure that the magneto-electric device is formed on either side of the first wafer, the first magnetic film is formed on the surface of the tapered groove portion formed on the other side of the first wafer, the second magnetic film is formed on the second wafer and the bonding portion is used to bond the second wafer having the second magnetic film formed thereon to in the surface of the first wafer. Therefore, the magneto-electric device is sandwiched between the magnetic films. Hence it follows that the external magnetic field can efficiently be converged to the magneto-electric device portion by the first and second magnetic films. That is, the vertical magnetic field is converged to the right side and the reverse side of the magneto-electric device portion. Therefore, the sensitivity of the magneto-electric device in a weak magnetic field can furthermore be improved.
A magneto-electric device has the structure that the magnetic projecting portion includes a projection which project toward substantially perpendicular to the third and fourth surfaces.
The above-mentioned magneto-electric device has the structure that the projecting ridge portion which is formed substantially perpendicular to the right side and the reverse side of the magneto-electric device portion is provided for the leading end of the tapered portion. Therefore, a portion of the external magnetic field passes the ridge portion formed at the leading end of the tapered portion toward a direction which is substantially perpendicular to the right side and the reverse side of the magneto-electric device portion. Hence it follows that substantially all magnetic fields which penetrate the magneto-electric device are magnetic fields which are substantially perpendicular to the right side and the reverse side of the magneto-electric device portion. Therefore, the vertical magnetic fields can efficiently be converged. It leads to a fact that the sensitivity of the magneto-electric device in a weak magnetic field can furthermore be improved.
A magneto-electric device has the structure that a second groove portion is recessed from the third surface toward the first wafer, the magnetic projecting portion is formed on the second groove portion.
The magneto-electric device has the structure that the tapered portion is the trapezoidal groove portion formed by anisotropic etching.
A magneto-electric has the structure that a wafer projection is formed as recessing a portion of the fourth surface without recessing the other portion of the fourth surface which corresponding to the wafer projection, the magnetic projecting portion is formed on the wafer projection, and the wafer projection is formed into a trapezoidal shape, the portion of the fourth surface is recessed by anisotropic etching. Therefore, the vertical magnetic fields can be converged to the right side and the reverse side of the magneto-electric device portion. Hence it follows that the sensitivity of the magneto-electric device in a weak magnetic field can furthermore be improved.
The magneto-electric device has the structure that the tapered portion is the projection formed between two trapezoidal groove portions formed by anisotropic etching. Therefore, the vertical magnetic fields which are perpendicular to the right side and the reverse side of the magneto-electric device portion can be converged. Therefore, the sensitivity of the magneto-electric device in a weak magnetic field can furthermore be improved.
A method of manufacturing a magneto-electric device, the magneto-electric device including a semiconductor wafer defining a first surface and a second surface opposite to the first surface, the method includes the steps of:
providing a magneto-electric device portion to the first surface, the magneto-electric device portion outputting an electric signal corresponding to the magnitude of an eternal magnetic field;
forming a first groove portion recessed from the second surface toward the first surface;
forming a first magnetic film on the second surface and the surface of the first groove portion;
providing a second semiconductor wafer so that the magneto-electric device portion put between the first surface and a fourth surface of the second wafer, the second wafer including a third surface and the fourth surface opposite to the third surface; and
forming a second magnetic film at the second wafer, the second magnetic film located opposite from the first wafer with respect to the magneto-electric device portion;
wherein a bottom of the first groove portion is positioned adjacent to the magneto-electric device portion.
wherein the providing a second wafer step includes a step of bonding the first and second wafers by a bonding portion;
a step of forming a projection on the second magnetic film, the projection projecting toward substantially perpendicular to the third and fourth surface;
a step of forming a second recess portion etched from the third surface toward the first wafer, the second magnetic film formed on the second groove portion;
wherein the second groove portion is formed into a trapezoidal shape by anisotropic etching;
a step of etching a surround recess portion from the forth surface, the surround recess portion surrounding a wafer projection of the second wafer, the second magnetic film formed on the wafer projection;
wherein a top surface of the wafer projection is positioned adjacent to the magneto-electric device portion;
wherein the wafer projection is formed into a trapezoidal shape, the surround recess portion is etched by anisotropic etching;
wherein a width of the first groove portion becomes short toward the magneto-electric device portion.